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Menarche — pronounced “meh-naa-kee” — is the first time a person menstruates. In other words, the first time they have a period.

Described as “the most definitive sign of puberty” in people with a uterus and vagina, it occurs around every 28 days and lasts for between 2 and 7 days each time.

Menarche (and every period thereafter) is controlled by rising estrogen levels that result in the uterus lining becoming thicker and an egg being released from the ovaries.

If the egg isn’t fertilized with sperm, the uterus lining breaks down, with the blood and tissue exiting the body via the vagina. This bleeding is called a period.

Anyone with a uterus and vagina is likely to experience menarche —unless they have a condition that prevents the process.

Amenorrhea is the absence of menstrual bleeding.

Primary amenorrhea occurs when a person with a uterus and vagina doesn’t experience menarche by the age of 15. Secondary amenorrhea occurs when a person has experienced menarche and later does not have a period for 3 months or more.

Common causes of amenorrhea include:

  • Using hormonal birth control, such as birth control pills
  • Taking certain medications, such as antidepressants, antipsychotics, and allergy medications
  • Having a low body weight
  • Engaging in excessive exercise
  • Experiencing periods of high stress
  • underlying conditions, such as polycystic ovary syndrome (PCOS)

Menarche symptoms tend to be similar to the usual period symptoms.

Before or during, you may experience the likes of:

All of these form part of premenstrual syndrome (PMS). But some people may not feel any of these, only experiencing the bleeding itself.

The first period, or the onset of menarche, may only last a few days and be quite light. The blood may look red, pink, or brown and may have clumps in it. Everyone is different.

After your first period, you may experience different symptoms leading up to menstruation and your periods may be heavier. Plus, it may take a while for your periods to become more regular.

The age of menarche has been decreasing over the past century. Why? According to researchers, better nutrition may be the answer.

Most people with a uterus and vagina now experience menarche between 12 and 13 years old.

But it’s also common to have your first period at a slightly earlier or later age due to the likes of family history, diet, and race.

Either way, it tends to happen around 2 years after breast or chest tissue starts to develop and around 6 months to a year after you notice a mucus-type vaginal discharge.

If menarche occurs before a person turns 9, it’s considered to be early.

But it’s not clear what exactly causes early menarche. And in most cases, no specific cause is found.

It can just be something that runs in your family. But health conditions involving the brain, ovaries, or thyroid gland can also cause early menarche as a result of sex hormone overproduction.

Menarche isn’t usually considered late or delayed until 15 years of age or if it’s been more than 5 years since breast or chest tissue began to develop.

Just like early menarche, figuring out the cause of delayed menarche isn’t always easy or possible.

Family history may play a role along with the likes of malnutrition, anemia, and autoimmune diseases.

There may be conditions involving the ovaries, too, where few or no hormones are produced.

A link between intense physical exercises, such as athletics or gymnastics, and delayed puberty has also been reported.

The effects of such training are thought to lead to gonadotropin deficiency —hormones involved in growth and sexual development —which results in low estrogen production, delaying puberty, and therefore menarche.

There are plenty of ways to manage periods. But finding the right way for you may take some experimenting.

To soak up the blood, you can try the likes of:

Some are more convenient than others and you may want to use more than one type of period product. For example, some people use tampons during the day, pads at night, and cups for activities like swimming.

Consider keeping one or more of the above in your bag in case your period shows up unexpectedly along with fresh underwear and an over-the-counter pain reliever like ibuprofen.

You may also want to track your periods via a standard calendar or special app like Clue or Flo to have a better idea of when they’re due. (But remember that it’s typical to have irregular periods for a number of years after your first.)

Pain relievers and heating pads are ideal tools for cramps and other period pains. But if you’re finding period-related symptoms difficult to cope with, consult with a doctor or other healthcare professional.

There is no evidence of sexual activity contributing to menarche in any way, including the onset of it or its delay.

Some researchers have found a correlation between the age of menarche and first sexual intercourse, with people experiencing menarche at 13 or younger being 2.6 times more likely to have partner sex for the first time before the age of 16 in one study.

However, other research has found no such association.

The only accepted link between sex and periods is that sex can delay your period if you become pregnant.

Menarche is a sign of maturation for people with a uterus and vagina. But it doesn’t necessarily mean that from then on, you can ovulate and become pregnant.

Some people may be able to become pregnant before experiencing their first period as hormones that trigger ovulation can be released beforehand.

And in other cases, ovulation may not occur for months or up to 2 years after menarche.

It’s also important to remember that you can become pregnant if you have penis-in-vagina sex while on your periodeven if it’s the first period you’ve ever had —and that some sexually transmitted infections (STIs) can be transmitted through contact with blood.

Barrier methods such as condoms can help protect against pregnancy and the transmission of STIs.

Ultimately, your period can be the most obvious sign that you’re not pregnant. So if it’s more than a week late and you’ve had sex without proper contraception, consider taking a pregnancy test.

If you’re worried about anything at all, healthcare professionals are there to help.

You may want to see one if you’re reaching later in your teens and haven’t yet had a period or if you’re struggling to deal with the symptoms and flow of the periods you are having.

Common advice is to speak with a healthcare professional if you haven’t had a period by the age of 15 or if you’re having to change your period product every 1 to 2 hours due to heavy bleeding.

Bleeding that lasts more than a week or that occurs in between periods as well as symptoms like dizziness, severe cramps, and a racing pulse are further signs that you should consult with a clinician.

Finally, if your periods are regular and then become irregular or don’t show any regularity after a couple of years, it’s worth chatting with a professional to see if there are any underlying causes.

Menarche can be a confusing experience that can feel and look different for everyone, requiring a bit of experimentation to manage.

But although it’s a natural part of development, it’s not necessarily a sign that your body is now able to become pregnant.

So if you’re sexually active, it’s important to use adequate protection. And if you have any period-related concerns, seek advice from a healthcare professional.

Lauren Sharkey is a U.K.-based journalist and author specializing in women’s issues. When she isn’t trying to discover a way to banish migraines, she can be found uncovering the answers to your lurking health questions. She has also written a book profiling young female activists across the globe and is currently building a community of such resisters. Catch her on Twitter.